Common channel signaling networks, such as the Signaling System 7 (SS7) based signal system, use dedicated channels to pass digital messages between systems for call setup, call control, call routing, and other functions. These dedicated signaling channels are part of a network that is separate from the network that carries the actual voice and data signals. An SS7 network is a separate switching system which is used prior to, during, and at the end of an actual voice or data call. The SS7 network is used to route control information. Whenever two switches or elements have to pass call control information during or prior to a phone call, they pass this data via the SS7 signaling network.
There are three basic types of network node elements in an SS7 network. One of them is the Service Switching Point (SSP), which may be a central office switch, a tandem switch or an end office switch. A second principal node element is the Service Control Point (SCP). An SCP acts as a database query server for the rest of the network. An SCP is used in such applications as translating ported telephone numbers, routing 800 calls, tracking roamers in a cellular network, and Alternate Billing Service/Line Identification Database services (or ABS/LIDB) which provide operator-type services. The third principal node element is the Signal Transfer point (STP). An STP is essentially a packet switch that routes the messages from SSPs and SCPs to SSPs and SCPs.
It is possible to combine these three different types of nodes into a single node. However, in North America, they are typically not combined. An SSP performs only switch functions, an SCP only control functions, and an STP only signal transfer functions. In European telecommunications systems, all of these different functions may be combined into one node.
The SS7 network carries a great deal of information and is extremely critical to the operation of the phone system. If an SS7 network is not functioning, or if portions of it are not operating, the phone system simply cannot deliver phone calls, even though all of the voice circuits are operating properly. The capacity and complexity of the SS7 network is small in terms of circuitry and bandwidth utilized by an end user compared to previous voice and data networks. The circuitry of the SS7 network is therefore much more critical. The actual elements in the SS7 network do not provide all the information required in network operations to manage and to determine the health and state of an SS7 network. It is therefore necessary for the telephone industry to deploy surveillance equipment to monitor the links connecting the nodes of the SS7 network.
The topology of the network is such that STPs are typically deployed in a mated pair configuration at geographically separate locations. Connected to a mated pair of STPs will be a set of SSPs and SCPs. This conglomeration of SSPs, SCPs and mated Pair STPs is called a cluster. Clusters are then connected by D-Quad links between STP mated pairs.
When any transaction or message is sent between two different devices on the network, it is often the case that the messages going from switch A to switch B travel one route on the network while the messages going from switch B to switch A travel a different route. The network surveillance equipment that monitors the link is designed to capture and correlate as much signaling information as possible regardless of network activity. Because of the different data paths that messages may take, it is difficult to do this correlation above what is called the transport layer when monitoring links at the STP sites. An example of an application level problem would be where a subscriber has a problem getting his/her calls delivered. The telephone company may attempt to fix the problem by doing a trace of all data pertaining to that subscriber's phone number, but the data may not all be located at one point. The data may be all in one STP, or split in some fashion, partially in one STP and partially in the other STP of a mated pair, which may be in a different city many miles away.
Automated monitoring equipment that continually monitors, in real time, the delivery of all calls over the signaling network is disclosed in U.S. Pat. No. 5,592,530, entitled TELEPHONE SWITCH DUAL MONITORS, the disclosure of which is hereby incorporated by reference herein. The monitoring system disclosed in U.S. Pat. No. 5,592,530 is capable of tracking the number of calls that are abnormally dropped, or the number of calls that have abnormal completion. The monitoring system uses a distributed state machine that captures all of the SS7 messages within a mated pair cluster and correlates the fragmented SS7 messages pertaining to a particular call or transaction to a single data record. Furthermore, the system filters out redundant or unnecessary SS7 messages in order to compile call transaction records containing a minimum amount of essential data in order to evaluate overall system performance and to diagnose system errors when they occur.
The Telecommunications Act of 1996 mandated the implementation of Local Number Portability (LNP), which allows telephone customers to keep their current telephone numbers when they change telephone service providers. There are three types of LNP: service provider portability, location or geographic portability, and service portability. Service provider portability allows customers to keep their telephone numbers when they change local service providers. Geographic portability allows customers to keep their telephone number when they move outside the area covered by their current end office. Service portability allows customers to obtain telephone services from another switch without changing their telephone number. LNP in effect permits customers to "own" their telephone number and gives them the capability of changing service providers and services without worrying about having to change their telephone number. Also, LNP opens the way for new entrants in the telecommunication market to compete with the existing local service providers.
In order to implement LNP, a database is used to store routing information for customers who have moved from one local service provider to another. The LNP database typically is connected to the network as an SCP. The LNP SCP is accessed by the network STPs to determine the directory numbers of ported customers and the location routing numbers of the switch that serves the ported customers. LNP functionality is described in detail in BELLCORE specification GR-2936-CORE (Local Number Portability Capability Specification), the disclosure of which is hereby incorporated by reference herein.
The introduction of LNP creates problems for prior art monitoring systems. One problem created by LNP is the possibility that a query message for a single call may be detected at the same STP more than one time. This situation may occur if a query message travels through an STP in one direction from a Signaling Point (SP) to an LNP SCP and then travels through the same STP in the opposite direction from the LNP SCP to the SP. The STP will detect the query message for the transaction as it passes in each direction. Another problem can occur when multiple query messages are generated for a single call. In a two-leg call or transaction, a first query message may be generated by the end office, SP, or SSP, when a call is initiated, and a second query message, having a different identifier, may be generated by an LNP SCP. As a result, monitoring units may detect, at one or more STPs, multiple messages for a single call or transaction. This complicates the prior art monitoring system's capability to correlate the messages into a single call record.
The prior art network monitoring systems are not able to correlate multiple detections of a single query message that passes through the same network element more than once. Also, prior art systems are not equipped to correlate multiple messages, having different identifiers, that correspond to a single call or transaction. Instead, prior art systems merely monitor messages at a single network element. The problem of correlating messages captured by more than one monitoring unit is complicated by the introduction of LNP, or other services, in which multiple messages having different identifiers may be initiated for a single call or transaction as a result of LNP queries. On the other hand, as described above, the same message may pass through a single node multiple times, in a different direction each time, as the message passes between end offices and LNP databases.